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Abstract. Bacterial carbonate formation includes autotrophic pathways that induce local C02 depletion of the medium and heterotrophic pathways that can lead to active or passive precipitation. In active precipitation, solid carbonate is localised by ionic exchange through the cell membrane. In passive precipitation, processes such as ammonification, dissimilatory nitrate reduction, degradation of urea or uric acid, and sulphate reduction lead to carbonate and bicarbonate production and a pH increase, processes which induce solid carbonate precipitation. In heterotrophic bacterial communities, pathways of carbonate precipitation always appear to be responses to enrichment by organic matter, and the precise nutritional conditions play a major role in the relationships between bacteria and the developing crystals. Heterotrophic bacterial precipitation, evaluated by laboratory experiments, appears to be the most probable process in the formation of apparently abiotic limestones. Bacterial carbonate formation has applications for stonework preservation and restoration.

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Abstract:The biomineralisation process is based on the ability of certain bacteria to produce solid Ca-carbonate. The scientific background is first presented, as far as aerobiotic metabolic pathways, biological processes and solid products are concerned. The process which consists in letting bacteria produce a carbonate protecting scale (biocalcin) on treated surfaces was developed through laboratory and life-size experiments. It is to date applied on buildings at the industrial scale. The process was also applied to statuary. Lastly, further microbiotechnical developments for restoration of limestone works of art are presented.

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